This invention relates generally to a micro-printer, and in particular to a micro-printer of low power consumption including a one piece molded plastic frame. In conventional printers which use metal frames, miniaturization beyond a certain point becomes difficult as it is necessary to provide screws, snap rings and the like for securing the frame. In addition, special processing required is inefficient and often involves plating, heat treatment and the like. As a practical matter, one such conventional printer, such as an electronic table calculator with a metal frame is heavy and can only be utilized as a table model due to its heavy weight.
Accordingly, it would be desirable to provide a miniaturized printer which overcomes the above noted shortcomings of conventional printers using metal frames. It should be noted that this cannot be accomplished simply by substituting a one piece molded plastic frame in place of the conventional metal frame. That is to say, for purposes of making a printer main frame of one piece by using plastic, it is necessary to satisfy two extremely important conditions. The first is that the printer be one which can be driven by low power consumption. This is required because the rigidity of a plastic frame is not as great as a metal frame. The resistance to the coefficient of pressure and velocity (hereinafter referred to as PV-value) on shafts or bearings which are molded into the one piece frame must be small. Thus, it is necessary to reduce or average the load required for the main operations of a printer, such as character selection, printing, paper feeding, etc. in a printer arranged in accordance with the invention. In addition, a printer with a one-piece molded plastic frame must be capable of being extremely small in size. If a one piece molded plastic frame of the same size as a conventional metal frame is employed in place of the conventional metal frame, significant problems will arise. For example, the cost of materials will increase due to the large size, and molding costs increase because individual molds are large and it is not possible to use a mold having multiple cavities. In addition, the molding shot cycle is long because it takes substantial time for pouring the material into the mold and chilling it. Thus, merely substituting a plastic frame would result in a product which is inferior to the metal frame in terms of manufacturing costs.